No Virginia, It Was Not The Throttle Body

[zeebaloo]

Hello all,

I am new to this forum. My usually reliable 98 lexus LS 400 has had developed surging idle, stalling, and hesitation upon acceleration problems. After reading seemingly simple descriptions of cleaning the MAF and Throttle Body, and the inspirational testimonials of the wonders that it does, I decided to try it myself. It was indeed easy (and I am no mechanic), but it did not solve my problems at all. I took her to the mechanic who told me I needed a new Throttle Body (a $1400 job... OUCH). So, I tried to replace it myself. That part alone cost me $1100 before tax. (still ... OUCH). I finally completed the replacement, but, the same problems still occur. I took it to the mechanic who told me, that I seemed to do it right, and he did not know why the problem still persists. He said it does not seem to be an electrical problems like continuity, but maybe I need a new ECM. He said that the ECM seems to be ignoring the O2 sensors and making the fuel way too rich. For a new ECM ... $1300.00

I did not bite, I took the car home and it sits waiting for me.

Before I take another $1300 plunge, is there anything else to do?

Another post recommended reflash my ECM, but my local lexus dealer repair dept says he has never heard of this before, let alone done that.

I was thinking to buy an OBD II reader, but two mechanics had done that, it did not help them.

One more thing, this problem is intermittent. Sometimes it dissapears for a 30 minute ride, then it comes back again. It seems to happen more when its hot, but I have seen it happen when the engine is cold.

Any ideas on how to proceed? Please advise.

[dcfish]

Hello all,

I am new to this forum. My usually reliable 98 lexus LS 400 has had developed surging idle, stalling, and hesitation upon acceleration problems. After reading seemingly simple descriptions of cleaning the MAF and Throttle Body, and the inspirational testimonials of the wonders that it does, I decided to try it myself. It was indeed easy (and I am no mechanic), but it did not solve my problems at all. I took her to the mechanic who told me I needed a new Throttle Body (a $1400 job... OUCH). So, I tried to replace it myself. That part alone cost me $1100 before tax. (still ... OUCH). I finally completed the replacement, but, the same problems still occur. I took it to the mechanic who told me, that I seemed to do it right, and he did not know why the problem still persists. He said it does not seem to be an electrical problems like continuity, but maybe I need a new ECM. He said that the ECM seems to be ignoring the O2 sensors and making the fuel way too rich. For a new ECM ... $1300.00

I did not bite, I took the car home and it sits waiting for me.

Before I take another $1300 plunge, is there anything else to do?

Another post recommended reflash my ECM, but my local lexus dealer repair dept says he has never heard of this before, let alone done that.

I was thinking to buy an OBD II reader, but two mechanics had done that, it did not help them.

One more thing, this problem is intermittent. Sometimes it dissapears for a 30 minute ride, then it comes back again. It seems to happen more when its hot, but I have seen it happen when the engine is cold.

Any ideas on how to proceed? Please advise.

Did a new TPS come with the new throttle body ?

[SW03ES]

Does the LS have an idle air control valve? Could be that...

[zeebaloo]

Does the LS have an idle air control valve? Could be that...

I saw those posts too. I dont believe the 98 LS400 has an IACV. I checked for that, looked in the pdf manual and asked local parts dept. I could be wrong, I am not a mechanic by trade.

I was thinking of maybe changing the o2 sensors. I wouldn't expect that bad sensors would make so much trouble.

[zeebaloo]

Yes, the TPS came attached to it. Also the throttle control motor and clutch. It was a good thing because I could not remove those things from the old one without striping the screws.

One parts warehouse wanted to sell me a throttle body for 800 with those things not included, I opted for the dealer's complete assembly.

Do you think there is something I need to adjust?

[joe913]

Has there been an OBDII scan? Do you have codes? Might be a good step before changing the O2 sensor or anything else for that matter. Some AutoZone stores will do a free scan. Good luck!

[SW03ES]

I'm going to put this in the LS forum, I just realized it was in the wrong place. You'll get more responses in there...

[ravig292]

i have a 2000 ls400 which is the same car as your 98

i had a problem where my car stalled on low rpms and when i accelerate the car hesitates to accel.

one day my car doesn't start i got it towed to lexus and they said the fuel pump went bad so they changed the whole fuel system.

once they did that all of those problems went away.

so your fuel pump may be going bad and you might need a new one.

you can get a new one here

http://www.parts.com/oemcatalog/index.cfm?...playCatalogid=0

[killerFatty]

Does the LS have an idle air control valve? Could be that...

I saw those posts too. I dont believe the 98 LS400 has an IACV. I checked for that, looked in the pdf manual and asked local parts dept. I could be wrong, I am not a mechanic by trade.

I was thinking of maybe changing the o2 sensors. I wouldn't expect that bad sensors would make so much trouble.

BTW the 98LS as well as every other vehicle with the 1UZ-FE(ALL 89-00 LS) has an IACV. It's located on the front of the intake manifold and is circular in shape with a couple hoses running to it. It may be partailly covered up by the piece of plastic covering the wires that connect the two ignition rotors.

[zeebaloo]

... and they said the fuel pump went bad so they changed the whole fuel system.

once they did that all of those problems went away.

so your fuel pump may be going bad and you might need a new one.

...

Thanks, this would be a whole new direction to go in. I will pull the codes tomorrow and see what comes up.

[zeebaloo]

BTW the 98LS as well as every other vehicle with the 1UZ-FE(ALL 89-00 LS) has an IACV. It's located on the front of the intake manifold and is circular in shape with a couple hoses running to it. It may be partailly covered up by the piece of plastic covering the wires that connect the two ignition rotors.

Hmmm, nice, another thing to check. The parts dept. guy and I could not seem to find it (looking over the diagrams). I will check the pdf manual. Searching thru that is sort of hit and miss. There does not seem to be a hyperlinked index.

[curiousB]

Rough idle is most commonly dirty throttle body or IACV. All cars with fuel injection have an IACV. Every one. The manufacturers my call it other things buts its function is mandatory in EFI systems.

I would spend a little more time diagnosing the root cause rather than guess and replace. As you now know this is kind of an expensive way to get to a final fix. Try the obvious things first. The IACV should be checked and cleaned. It may not be the problem but it will cost you only your time, some cleaner fluid, and old rags to rule that out.

[zeebaloo]

Rough idle is most commonly dirty throttle body or IACV.

Ok, fair enough, so I am having surging idle (rpm going up and down) and when its in Drive, the fluxuation gets so low that it stalls. I dont know whether one would consider that rough or not,or it would have to cough which it does not do.

[eatingupblacktop]

Rough idle is most commonly dirty throttle body or IACV.

Ok, fair enough, so I am having surging idle (rpm going up and down) and when its in Drive, the fluxuation gets so low that it stalls. I dont know whether one would consider that rough or not,or it would have to cough which it does not do.

A couple of other possibilitiies:

A dirty/sticking ISC. Solution would be to clean it to see what change it woudl make or if it needs replacing.

Another cause could be leaking vacuum. Especially between the AFM and the manifold. The ECU hunts to correct the bad fuel slope because the leak changes the mixture that the AFM is reporting. The IACV is used by the ECU's fuel map in an attempt to adjust for the overly lean/rich oscillation. If the amount of the leak is sizeable, the O2 sensors will enrich the mix and send the revs up. As the revs climb the leak is overcome and the mix is leaned out, which brings the revs back down where the whole sequence is repeated. Check all your vacuum hoses and connections.

[zeebaloo]

BTW the 98LS as well as every other vehicle with the 1UZ-FE(ALL 89-00 LS) has an IACV. It's located on the front of the intake manifold and is circular in shape with a couple hoses running to it. It may be partailly covered up by the piece of plastic covering the wires that connect the two ignition rotors.

To further beat a dead horse, I bought a manual (a non-hyperlinked set of pdfs) for the ls400 (1998-2000) and did a search on "iac","isc", "idle air control" and "idle speed control", nothing turned up. Maybe it could be part of a graphic and not searchable, but it seems that it is just not mentioned. This is what led me before to believe that it may not have one. So if someone has a picture of this, it would really help. :)

[curiousB]

IACV

Y1BSh

[SW03ES]

Yeah leaking vacuum, even very slightly could be the issue but I'll tell you what, I bet its the IACV. My parents have a 97 Explorer that they use as a third car that was having some stalling issues when cold and in general a rough idle. We replaced the IACV ($80 and 15 minutes...sure its not that cheap or easy on the Lexus) and it fixed it right up. Depending on what the IACV costs I would probably just replace that first, if the throttle body was dirty enough to require replacement, you can bet the IACV is filthy too.

I know you can clean them, but I'd spring for a new one to compliment the nice new throttle body.

[zeebaloo]

IACV

Wow, thanks, but this is not my engine. It looks like an RX. I have only one TB and there is no IAC inside the barrel.

[zeebaloo]

IACV

I will check, this doesnt look like my engine, but I will confirm.

Yep, this looks like an RX300. My LS400 TB assembly looks nothing like this.

[dcfish]

Yeah leaking vacuum, even very slightly could be the issue but I'll tell you what, I bet its the IACV. My parents have a 97 Explorer that they use as a third car that was having some stalling issues when cold and in general a rough idle. We replaced the IACV ($80 and 15 minutes...sure its not that cheap or easy on the Lexus) and it fixed it right up. Depending on what the IACV costs I would probably just replace that first, if the throttle body was dirty enough to require replacement, you can bet the IACV is filthy too.

I know you can clean them, but I'd spring for a new one to compliment the nice new throttle body.

I agree with SW, Maybe a vacuum line was cracked or creased while you removed the TB and/or replaced it, Make sure all of the vacuum lines are connected to there proper position and fully tight.

[zeebaloo]

Has there been an OBDII scan? Do you have codes? Might be a good step before changing the O2 sensor or anything else for that matter. Some AutoZone stores will do a free scan. Good luck!

The story continues ... I bought a scanner because the pep boys were never avail to pull the codes. 55 bucks, hopefully a good investment.

The codes are;

P0172 - Too rich bank 1 (something like that)

P1780 - Park Neutral Position switch Malfunction

P0133 - P0133 Lazy O2 Sensor Bank 1 Sensor 1

P0500 - which I believe is speed sensor. But, today when limping along, started to feel some transmission jerks. Not sure whether this is a symptom or cause.

[zeebaloo]

...bump...

So as it stands now, there is no good pointer to the location of the IACV for a 98 (I say 98) LS400. Until now, all pics have been from RX300 (Not to sound ungrateful for the attempted help), and I have since pulled the computer codes, I had already purchased pdf manual sets, so far they dont point me to said valve.

I dont believe there are vacuum leaks, the mechanic would have probably found it. My thinking now is to proceed to replace 02 sensors.

would like to hear from any LS owners with IACV exp.

[curiousB]

This link might be helpful. Not sure it is the same IACV as yours but might help you find yours.

http://planetsoarer.com/IAC/iac.htm

[killerFatty]

hear is a good pic.

[blake918]

To further beat a dead horse, I bought a manual (a non-hyperlinked set of pdfs) for the ls400 (1998-2000) and did a search on "iac","isc", "idle air control" and "idle speed control", nothing turned up. Maybe it could be part of a graphic and not searchable, but it seems that it is just not mentioned. This is what led me before to believe that it may not have one. So if someone has a picture of this, it would really help. :)

All of the photos so far have not been of a 98-00 LS 1UZFE VVTi engine, so here are some pics of my engine, and maybe someone can point to it on there. After rummaging through my PDFs, I did find some relating to this. I kind of thought it might not have one either since I couldn't see it either, but it looks like it's hidden if I'm looking at the PDF right.

CI__IACV_Control_.pdf

COMP.pdf